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Biomedical subjects

D C Watts

Publications and source records attributed to D C Watts.

At least 55 records · Page 3Linked to original sources
PubMed1999

Development of noncarious cervical notch lesions in vitro.

PURPOSE: The initiation and progression of noncarious cervical notch lesions (NCCL) continues to perplex clinicians worldwide and poses a considerable restorative challenge. The purpose of this brief communication is to report what is believed to be the first in vitro production of notch-shaped lesions in the cervical third of premolar teeth. MATERIALS AND METHODS: The lesions, were produced by axial loading of selected permanent premolar teeth in a 10% aqueous solution of sulfuric acid over a period of 5 days, followed by immersion in water for 7 days. RESULTS: Results revealed macroscopic and microscopic features similar to those observed in noncarious cervical lesions in vivo. The lesions were incidental findings while the authors were studying stress corrosion of enamel at low pH. Although much remains to be investigated regarding the etiology and pathogenesis of NCCL, axial loading and a corrosive environment may be implicated in these processes. The artificial lesions arose in clinically sound teeth, suggesting that there is no simple clinical examination to identify teeth at risk from NCCL. CLINICAL SIGNIFICANCE: The relationship between the development of NCCL and applied stress indicates that occlusal factors may play the most significant role in the initiation and progression of NCCL.

Bicuspid↗
PubMed1999

Occlusal registration: science or art?

Most of the information available to guide the clinician in making occlusal records focuses on the clinical techniques and methods involved. There is little objective information regarding the use of the more recently introduced elastomeric materials which are growing in popularity in the clinic. Much of the published work relies on the clinical experience of the authors rather than the properties of the material to be used to make the occlusal records. This paper aims to review the materials currently available to clinicians for use in occlusal registrations. The materials are discussed with regard to their suitability for the task and suggestions given regarding their use. Setting aside considerations of technique, it is suggested that there would be value in basing the selection of materials for occlusal registration on objective research. However, it may well be that the technique, as with many other things in dentistry, is as important as the specific properties of the materials used.

Dental Impression Materials↗
PubMed1999

Demonstration of "vertical barrelling" using profilometry.

The aim of this study was to demonstrate the extent of tooth flexure under axial loading using profilometry. Fifteen extracted human permanent upper premolar teeth were embedded in hard die stone and divided into 3 groups. One group was left unprepared, the second group had artificial cervical saucer shaped lesions prepared and the final group had artificial cervical notch lesions prepared. The labial profile was taken using a diamond stylus mounted in a Profilometer. The teeth were then loaded in an axial direction to circa 670 N and the labial surface re-profiled 20 s after loading. The results indicate that changes occur in the labial profile of premolar teeth that are subjected to axial loading which could be considered to represent vertical barrelling. Changes in the profile of the artificial saucer and notch lesions prepared at the cervical region suggest that stresses would be generated on restorations of these lesions.

Bicuspid↗
PubMed1998

Ambient light working times of visible light-cured restorative materials. Does the ISO standard reflect clinical reality?

OBJECTIVES: The aim of this study was to determine whether a custom built light box could reliably reproduce clinical conditions and whether the current ISO standard test for the working time of visible light cured (VLC) materials (ISO. Dental Resin-based Restorative Materials. ISO:4049, 1991) reflected clinical reality. METHOD: The ISO test requires a VLC material to remain homogenous after exposure to an 8 kLux light source for 60 s. The relationship between the intensity of ambient lighting and the working times of visible light-cured (VLC) restorative materials was investigated by exposing 23 different VLC composite resin materials to a range of light intensities and measuring the working time in seconds: (a) under clinical operating conditions; (b) in a custom light box at 24 kLux; and (c) at 8 kLux in the light box. Working times were determined by placing 0.06 g samples between two glass plates and gently rotating until clefts or voids appeared. RESULTS: Clinical lighting conditions (24 kLux) gave a mean working time of 54 s (s.d. 14 s). In the light box at 24 kLux the mean working time was 54 s (s.d. 11 s). At 8 kLux (under otherwise identical conditions) the mean working time was 162 s (s.d. 49 s). SIGNIFICANCE: A 24 kLux illuminance in the laboratory gives an optimal correspondence to operative lighting conditions. This is three times the lighting level required for ISO purposes, and gives more realistic working times.

Analysis of Variance↗
PubMed1998

Analysis of reactions in glass-polyalkenoate/resin systems by dielectric impedance spectroscopy.

The principles of impedance spectroscopy are surveyed, with consideration of both low and high impedance dielectric biomaterials where the response mechanisms are dominated, respectively, by dipolar relaxation and ionic charge migration. The situation of dental biomaterials is considered with special reference to glass-ionomer polyelectrolyte systems and to the impedance changes that may arise in consequence of setting mechanisms. Measurements have been conducted using both static and frequency-dependent potentials; where appropriate, with a high impedance interface and frequency-response analyser. Data are presented for the control situation of poly(methyl methacrylate) (PMMA) and for a series of glass-ionomer and resin-modified glass-ionomer biomaterials. It is observed that in the glass-polyalkenoate (G-PA) materials, ionic conduction and polarization are the dominant factors contributing to the impedance. This contrasts with the dipolar relaxation characteristic of PMMA. It is concluded that a more extended programme of data-acquisition is required, where possible from a 'homologous' series of formulations, to lay a firm foundation of mechanistic interpretation.

Biocompatible Materials↗
PubMed1998

Dental materials: 1996 literature review.

This critical review of the published literature on dental materials for the year 1996 has been compiled by the Dental Materials Panel of the UK. It continues the series of annual reviews started in 1973 and published in the Journal of Dentistry. Emphasis has been placed upon publications which report upon the materials science or clinical performance of the materials. The review has been divided by accepted materials classifications (fissure sealants, glass polyalkenoate cements, dentine bonding, dental amalgam, endodontic materials, casting alloys, resin-bonded bridges and ceramo-metallic restorations, ceramics, denture base resins and soft lining materials, impression materials, implants materials, orthodontic materials, biomechanics and image processing, resin composites and casting investment materials and waxes). Three hundred and thirteen articles have been reviewed.

Dental Alloys↗
PubMed1998

Dental materials: 1996 literature review. Part 2.

This critical review of the published literature on dental materials for the year 1996 has been compiled by the Dental Materials Panel of the UK. It continues the series of annual reviews started in 1973 and published in the Journal of Dentistry. Emphasis has been placed upon publications which report upon the materials science or clinical performance of the materials. The review has been divided by accepted materials classifications (fissure sealants, glass polyalkenoate cements, dentine bonding, dental amalgam, endodontic materials, casting alloys, resin-bonded bridges and ceramo-metallic restorations, ceramics, denture base resins and soft lining materials, impression materials, implants materials, orthodontic materials, biomechanics and image processing, resin composites and casting investment materials and waxes). Three hundred and thirteen articles have been reviewed.

Ceramics↗
PubMed1998

Effect of differing resin luting systems on fracture resistance of teeth restored with dentin-bonded crowns.

OBJECTIVE: This study investigated the effect of differing bonding and luting system combinations on the fracture resistance of teeth restored with dentin-bonded all-ceramic crowns. METHOD AND MATERIALS: Standardized preparations were carried out on five groups, each of 10 sound, unrestored, maxillary premolar teeth. Ceramic crowns were constructed, their internal surfaces were etched with hydrofluoric acid, and the crowns were placed with the following dentin bonding and resin-based luting system combinations: group A, Mirage ABC and Mirage FLC; group B, Metabond luting material; group C, All-Bond 2 and Duo-link; group D, Scotchbond MP Plus and 3M Indirect Porcelain Bonding Kit; and group E, All-Bond 2 and 3M Indirect Porcelain Bonding Kit. The restored teeth were loaded in compression at 1.0 mm/min. RESULTS: Mean fracture loads of 0.77 kN, 0.81 kN, 0.71 kN, 1.24 kN, and 1.03 kN were recorded for groups A, B, C, D, and E, respectively. Statistical analysis indicated that the mean fracture resistance of the restored teeth of groups D and E was significantly greater (P < .05) than that of the other three groups. CONCLUSION: The fracture resistance of dentin-bonded crowns used in this laboratory study was dependent on the bonding and luting systems used.

Analysis of Variance↗
PubMed1997

Changes of surface texture of enamel in vivo.

There are various methods of measuring tooth wear, including that which could be considered to be associated with acid erosion. However, the present systems are limited in that they require an extended period of study to detect wear and also they do not give any insight as to the underlying mechanism of the tooth tissue loss. The aim of this study was to use a profilometric measuring system analysing novel surface texture parameters normally associated with the automobile industry to describe the wear and run-in behaviour of machined sliding engine parts. The texture parameters selected were the traditional Ra parameter and also parameters derived from the bearing ratio. Analyses of the surface texture of the labial surface of upper central incisors at an interval of three months indicated that the enamel surface was smoother but there were subtle changes occurring to the enamel. There was a statistically significant increase in the depth of pits/pores of the enamel surface, which could be identified as sites of retention of exogenous acid or chelating agent. The effects of acid erosion are not uniform but are dependent upon several factors; the configuration of the enamel surface may play an important part in the mediation of acid erosion type lesions.

Adult↗
PubMed1996

The application of ESEM in dental materials research.

OBJECTIVES: To describe the use of environmental scanning electron microscopy (ESEM) to investigate acid etching of enamel and to comment on future applications of ESEM in dental materials research. METHODS: The acid etching of axially fractured specimens of human enamel by a 35% (ortho) phosphoric acid etchant was observed using ESEM. RESULTS: Most of the etching action, as evidence by gaseous bubbling in the etchant film, was observed to occur within 10 s of applying the etchant. High magnification examination of the etched areas revealed distinct etching patterns. CONCLUSION: ESEM may play an important role in developing the understanding and existing knowledge pertaining to dynamic chemical and physical interactions between components of restorative systems and tooth tissue substrates.

Acid Etching, Dental↗
PubMed1996

Surface texture changes of a composite brushed with "tooth whitening" dentifrices.

OBJECTIVES: The aim of this investigation was to evaluate the significance of selected surface texture parameters used to describe and quantify the effect of tooth brushing with various "tooth whitening" dentifrices on a resin composite surface in vitro. METHODS: Specimens of a microfil resin composite were brushed with selected dentifrices. Surface texture profiles were acquired and analyzed both pre- and post-brushing using a contact diamond stylus. The selected parameters chosen to describe the surface texture were Ra, Rz, Rpm and the Rpm:Rz ratio. Differences between toothpastes were assessed using an ANOVA and a multiple comparisons test, the Student Newman-Keuls procedure. P and t values were calculated to determine if any of the surface roughness parameters were significantly changed by brushing. RESULTS: The results indicate that there were significant changes in the surface texture of the resin composite following tooth brushing with the selected dentifrices. For example, the use of Clinomyn significantly increased the surface roughness of the resin composite, as measured by the Rz parameter, from 2.19 +/- 1.67 microns to 10.02 +/- 2.57 microns (p < 0.05). In addition, the surface texture parameters chosen to describe the properties of the surface should reflect a knowledge of profile shape such as Rpm:Rz ratio, and care should be taken if measurements of surface texture of dental restorative materials are to be used as predictors of clinical performance. SIGNIFICANCE: All the toothpastes chosen for this investigation left a surface on the resin composite which may be prone to crack propagation during "vertical barrelling" movements generated during mastication. However, this may be more of a function of the rigidity of the restorative material rather than the surface left after tooth brushing.

Analysis of Variance↗
PubMed1996

Colour changes in acrylic teeth--comparison of an objective and subjective method.

Colour changes in four currently used brands of acrylic dental teeth were measured objectively and assessed subjectively following the application of heat, acrylic monomer and light. The data indicated that no clear correlation existed between the results of visual inspection and opto-electronic measurements. It is suggested that visual assessment is an unreliable method of detecting colour change, and an objective colorimetric method is therefore recommended.

Acrylic Resins↗
PubMed1996

Glove contamination of etched porcelain surfaces and bond strength to enamel.

PURPOSE: To investigate whether contamination of etched porcelain surfaces by operating gloves of different types alters the shear bond strength of the porcelain to a resin-composite luting material. MATERIALS AND METHODS: Fifty porcelain specimens of 7 mm diameter and 2 mm thick were manufactured in feldspathic porcelain. After randomly dividing the specimens into five groups of 10 specimens, the porcelain surface of each specimen was etched with hydrofluoric acid. Samples of glove material, taken from the outer surface of gloves typically used in clinical dentistry, were held against the etched porcelain surface for 10 seconds. Four different glove types were used, Group 1: Biogel D; Group 2: Featherlite; Group 3: Microtouch; and Group 4: Tru-Touch; Group 5: Control/not treated with glove material. A resin composite-based luting material of standard shade was placed against the treated porcelain surface in a PTFE mold of 2 mm diameter and 2 mm depth, and light-cured from a direction of 90 degrees to the porcelain surface for 60 seconds. Each specimen was tested in shear, the results noted and subjected to statistical analysis. RESULTS: The mean shear bond strengths (MPa) for Groups 1, 2, 3 and 4 were 22, 21, 16 and 23 and for the control group, 26. Statistical analysis of the results indicated that there was no significant difference between the groups.

Aluminum Oxide↗
PubMed1995

Mechanical behaviour and structure of light-cured special tray materials.

OBJECTIVES: This study relates some structural characteristics of representative special tray visible light cured (VLC) resin composites to their creep-recovery, hardness and flexural strength properties. VLC prosthodontic materials have not yet achieved the same acceptance as the VLC resin composites, perhaps because less is known of their structural and performance characteristics. METHODS: The VLC resin composites used were Triad, Convertray and Palatray. The inorganic composition was analysed quantitatively by heating known amounts of resin composite to 800 degrees C, and weighing the ash. Elemental composition was determined using X-ray microanalysis. Mechanical properties, including hardness, flexural behaviour and creep recovery, were obtained by standard methods. RESULTS: The inorganic filler content for Palatray was higher than that of Convertray or Triad, and the flexural modulus and flexural strength of Palatray were superior to that of Triad or Convertray. The mean maximum creep strain for the Palatray specimens was only 2.45% after 5 h loading under 37 MPa and there was a permanent set of 1.5% after 7 h recovery. CONCLUSIONS: Palatray exhibited superior overall properties and this evidently related primarily to the high volume fraction of filler.

Aluminum↗
PubMed1995

Comparison of methods for measuring surface roughness of ceramic.

The aim of this investigation was to compare two methods of assessing the surface texture of finished dental ceramic; a laser reflectivity method (LSR) and a contact stylus tracing method. Identical ceramic blocks (Dicor MGC) were finished using a variety of techniques and devices, and the surface texture characterized by LSR and contact stylus tracing to enable comparisons to be made between the two methods. The results indicate that there is little correlation between the two measuring methods. Therefore, laser reflectivity should not be exclusively used to measure the surface texture of contoured and finished ceramic materials. The development of sophisticated surface characterization parameters suggest that the surface characteristics of dental restorations and other related surfaces should be described using more than one surface measurement parameter. Surface parameters should be chosen which can both quantify surface roughness and provide information on the shape of the surface under investigation.

Dental Polishing↗
PubMed1995

Development and assessment of an objective method of colour change measurement for acrylic denture base resins.

Current standard specifications for the laboratory evaluation of denture base materials require subjective assessment of colour stability. This study evaluates a new objective measurement technique for translucent denture base materials, by comparing quantitative data with the results obtained from a standard subjective method. Preliminary work on three representative commercial acrylic materials resulted in the selection of a white background for the quantification of colour change of these translucent materials. One half of each sample was exposed to artificial sunlight for 24 h. The colour of both exposed and unexposed resin was measured on the CIE L*a*b* scale using a photo-electric colorimeter. Significant changes in the b* and E* values (P < 0.01) were observed following light exposure. Objective data for a wide range of commercial materials were compared with the results of a subjective evaluation and it was shown that a change in b* of 1.5 units was discernable subjectively by eye for 100% of the cases. It is suggested that this method and limit value could form the basis of a new objective colour change specification for polymeric dental materials.

Acrylic Resins↗